1. Field of the Invention
The invention concerns a method for determination of the position and/or position change of a measured object relative to a sensor, the sensor preferably having a sensor coil acted upon with alternating current. The invention also concerns a corresponding sensor arrangement.
2. Description of Related Art
Electromagnetic sensors are widely used in engineering. They are used, for example, to monitor the distance between a sensor and a measured object, to measure rotational or valve lift movements, to determine the position of a piston or to detect conducting objects. This incomplete list demonstrates the extensive use possibilities of this generic type of sensor.
A permanent magnet movable along a soft magnetic core is used as measured object in a path sensor known from DE 36 10 479 A1. Two oppositely exposed exciter coils and a secondary coil are wound around the core. Depending on the position of the measured object relative to the sensor, a virtual air gap is produced on one location of the soft magnetic core, which means that the voltage induced in the secondary coil changes with the position of the measured object. The voltage is proportional to the position of the measured object relative to the sensor.
A path measurement system comprising an inductive sensor, a transducer and an evaluation unit is known from EP 1 158 266 A1. According to one practical example a magnet whose position can vary relative to the sensor is used as transducer. The magnetic field of the magnet brings the soft magnetic material of the sensor into saturation. Because of this local saturation effect the inductance of measurement coil of the sensor changes, which is connected to an oscillator, whose frequency or amplitude changes are detected.
A magnetically operable path recorder with a magnetic field sensor and a magnet that can be displaced along a movement line is known from DE 203 07 652 U1. A bar of soft magnetic material is arranged parallel to the movement line from whose end the magnetic field sensor is arranged facing the end with its sensor device. The length of the bar and the width of the magnet determine the measurement range of the path recorder.
Sensors with magnetoelectric converters are used for contactless recording of a rotational movement of a rotor. Examples of this are known from U.S. Pat. No. 4,926,122 A, EP 0 729 589 B1 or DE 30 41 041 C2. In practice these converters are positioned very tightly against the measured object in order to guarantee immunity to disturbance. At these limited spacings (often on the order of 1 mm), the sensor, especially under real operating conditions, can be damaged. It is especially important in dynamic operation to achieve reliable recording of the rotational movement at relatively large base spacing.
Other sensors and proximity switches that exploit the saturation effect of soft magnetic materials of high permeability are know from DE 38 03 293 A1, DE 38 03 253 A1 or DE 36 10 479 A1. The response distance of such sensors, however, is limited. In order to achieve greater measurement ranges the evaluation circuit must have a high amplification factor. However, this leads to large temperature-related errors and high requirements on installation tolerance.
The underlying task of the invention is therefore to provide a method with which a position or position change of the measured object relative to sensor can be measured both in static and dynamic operation with high resolution. A corresponding device with the simplest possible design is also to be provided.